The memorial industry is based on the idea of permanency—that what you leave as a memorial will be there for the generations. Monuments that use granite or other hard stone last indefinitely. They are relatively unaffected by environmental factors such as heat, cold, ice, rain, snow, and Ultra Violet (UV) exposure. However, the paint or stain that is used to mark or beautify the stone is susceptible to these factors. Sometimes notable fading occurs even after a few years.
Fading and failing of a coating can occur due to a number of influences. Many coatings have a difficult time adhering to stone. UV exposure destroys and bleaches many colors and pigments, which causes fading over time. UV exposure degrades, and eventually destroys, the binder that clings the pigments to the stone. As the binder degrades, the paint or stain can go chalky and eventually flake or blister and wear off. Further, since the binder fails over time, some pigments, like carbon black (which resists fading) can leach or bleed into other areas. Lime particles from rainwater or irrigation water can then permanently trap the leached pigments onto the areas that were intended to remain unpainted.
In general, granite markers have a life expectancy of several centuries or even millennia. However, applied coatings (e.g., paint) can wither away in a much shorter period of time, for example, anywhere between three and 15 years. Coatings applied to sandstone or marble can fade even faster. Sandstone or marble markers erode such that they become chalky or sandy and become impossible to read the inscriptions.